Panties... But not hers?

A pink cloth greeted Anna as she unclutched her hand. As the door closed, she unraveled the garment and found that it was indeed panties. In any logical world they would be hers, but instead there was a noticeable fact that made it quite clear they weren't: they were dripping wet, stuck to her hand, and smelled of... something. Something that she couldn't quite place but smelt familiar.

A small part of her brain wanted her to use them to cover herself, but that was shouted out by the question that immediately plagued her mind: Where did they come from?

She glanced around the darkened room, trying to see if there was anyone that stood out, reballing the sticky garment as she did. And then, in the corner of her eye, she could make out someone, a girl, draped in shadow and hiding under a desk.